Rare subcutaneous metastases of papillary thyroid carcinoma revealed by ¹⁸F-FDG PET/CT

A 76-year-old woman underwent thyroidectomy in 2010 for a 5-cm papillary thyroid carcinoma (PTC), oncocytic variant, with extrathyroidal extension, followed by 150 mCi radioactive iodine therapy (RIT). During follow-up, locoregional recurrence, pulmonary metastases, and a paraesophageal metastatic lesion developed without significant thyroglobulin elevation under TSH suppression. After additional RIT, repeat surgery, and external beam radiotherapy thyroglobulin became undetectable; however, two consecutive increases in 2026, from 1.98 to 3.57 ng/mL, prompted ¹⁸F-FDG PET/CT, which demonstrated multiple FDG-avid subcutaneous lesions (Figure 1). Punch biopsy of a shoulder lesion confirmed metastatic PTC with a focal tall-cell component and BRAF positivity (Figure 2).